You might have noticed neatly arranged crushed stones on railway tracks during any of your travel by railways. Have you ever wondered why it is so? Let us explore the reason behind the certain arrangement of crushed stones on railway tracks here.
The crushed stones arranged are known as ballast and they arranged in the form of a bed, they are used in major railway networks in the world and are helpful in spreading the train's weight over a wide area, draining water instantly from the tracks and also provide the flexibility of shifting the stones as the track shifts.
What is a Ballast?
Ballast is a layer of hard, crushed stone that is placed below and around the wooden or concrete beams that hold the rail track apart. It sits between the sleepers and the ground forming the base the entire track rests on.
These rocks are mostly granite, basalt or quartzite as these are tough stones that can withstand high forces and vibrations that arise when a train crosses the tracks.
How Does Ballast Support the Weight of a Train?
A loaded train applies a great force to the rails which in turn applies pressure to the wooden beams called sleepers. The force from the sleepers are transferred to the ballast.
Ballast or the loosely arranged stones distribute the weight outward rather than focusing it on one point. Without ballast, the weight of rails will damage the rails by bending or crushing them.
How Does Ballast Help With Drainage?
Ballast or the loosely arranged stones have gaps between them, thereby making the rain water flow straight the bed of the ballast without accumulating around the sleepers.
Standing water is one of the easiest and the fastest ways to weaken the foundations of a rail formation. It happens because wet soil does not possess strength and therefore is not able to support the track evenly.
By draining the water quickly, the ballast keeps the ground below it dry and firm through every season.
How Much Ballast Does a Track Actually Need?
The ballast bed depth depends on the traffic and the speed of the line. For Indian Railways Broad Gauge Network, the recommended ballast cushion below the sleeper is 250 mm, and for the main lines it is 350 mm as they need to handle greater loads. These stones are machine crushed to be around 50 mm in size, since small pieces help in reducing drainage.
Do All Railway Lines Use Stone Ballast?
While ballast is the default choice for most railway tracks worldwide, some high-speed lines and metro systems around the world use concrete slabs instead of ballast, as they need little maintenance and retain their shape even at high speeds, but are more expensive than ballast.
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